The present invention is directed to a device for ejecting or taking in liquid or paste-like media as specified in the preamble of patent claim 1.
In joint surgery, where endoprostheses must be firmly joined to the bone, a bed is initially cut from the bone in which subsequently the prosthesis is secured by means of bone cement. In order to achieve a perfect bond between the bone cement and the bone, the bed must be flushed so as to be substantially completely free from bone residue (caused during cutting) or the like. Exhausting of the flushing liquid is a relatively critical operation and must be performed only at a relatively low negative pressure which should also be controllable.
Furthermore, the bone cement, which is a high-viscosity "two-component synthetic resin", must be introduced into the prepared bed and this operation also must be controllable.
CH-PS 546,075 discloses a manually operated device for introducing bone cement, which is configured like a commercially available hypodermic needle. But the operation of this device requires considerable energy.
In addition to that, devices are available which are designed similarly to the operating means for plastic cartridges and permit high-energy step-wise advance of a control piston via a lever provided on a pistol grip. But these devices are basically unsuited for ensuring continuous filling of the bone cement, thus resulting in non-uniform and therefore imperfect filling with bone cement.
The journal "med.-Orthop.-Techn." 6/86; p. 203, discloses a pneumatic device of the initially specified kind, in which the piston for ejecting the bone cement is actuated by compressed air directly through a piston-and-cylinder system so that bone cement can be ejected continuously and without undue effort by the operator. It is an essential problem of this device that the bone cement ejection rate (volume per unit of time) must be performed through a correspondingly sensitive actuation of valves which control the air supply to the actuating cylinder. It has been found that the operator must work with extreme care so that bone cement is uniformly ejected in the desired manner in response to its respective current viscosity (which varies with time). As the atmosphere in an operating room is well known to be frequently quite hectic, "operating errors" with fatal consequences may easily happen.
On the basis of the above-specified prior art it is the object of the present invention to improve a device of the initially specified kind in such a way that uniform ejection with little energy expenditure becomes possible.